The Berlin Wall seemed quite effective.
The Great Wall of China probably was as well. However there is no need to even build a wall along those parts of the border where the natural terrain is harder to get around than said wall. No offense, but I think it is a little disingenuous to suggest that a wall would not do any good at all.
As for ISIS, another attack here is inevitable. And at least some of the terrorists most likely will be U. S. citizens who have never left the country. Additionally, there might be a handful of terrorists that came across the border illegally. The majority of the terrorists though will probably be immigrants who came here legally from Europe.
We are at war with an ideology. Or better said, an ideology is at war with us. And in the Internet Age you can't really build a wall around ideas, at least not in a free society. So to say that a wall would stop ISIS from coming here is just as disingenuous as saying that a wall wouldn't do any good at all.
We may be tired of war, but our enemy is not tired of trying to murder us. As war-weary as we are though, I would still much rather fight them in Mosul than in Montgomery.
As for the mass shootings, that is a different problem entirely, although also an important issue to solve. But I think we solved that one already in another thread.